The present invention generally relates to an implantable atrial defibrillator for applying cardioverting electrical energy to the atria of a patient's heart in need of cardioversion. The present invention is more particularly directed to such a defibrillator which is programmable into a fully automatic mode, a patient activated mode, or a combined automatic and patient activated mode. The atrial defibrillator includes an intervention sequencer which is utilized in all of the selectable modes. The intervention sequencer includes an atrial fibrillation detector for determining if the atria are in need of cardioversion and a cardiovertor for applying cardioverting electrical energy to the atria of the heart.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected ventricular electrical activation (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistant to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality.
Two such proposed defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these proposed defibrillators required the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator with an external magnet. Neither defibrillator included an atrial fibrillation detector or detected atrial activity of the heart. As a result, these manually operated defibrillators provided no atrial fibrillation detection support for the patient.
An improved implantable atrial defibrillator which is automatic in operation is fully described in U.S. Pat. No. 5,282,837. The atrial defibrillator disclosed in this patent is truly automatic by including an atrial fibrillation detector which, responsive to sensed atrial activity, determines when the atria of the heart are in need of cardioversion. When the atrial fibrillation detector determines that the atria are in fibrillation and thus in need of cardioversion, the atrial fibrillation detector causes a cardiovertor stage to deliver defibrillating or cardioverting electrical energy to the atria in timed relation to a detected ventricular electrical activation (R wave) of the heart. As a result, the atria are automatically and safely cardioverted.
Because atrial fibrillation, unlike ventricular fibrillation, is generally not immediately life threatening, a fully automatic atrial defibrillation modality may not be necessary for a great number of patients, and especially for those patients who are highly symptomatic. Further, some patients may wish to control when cardioverting therapy is to be delivered. However, even though some patients may be able to accurately diagnose when their heart is experiencing an episode of atrial fibrillation, it would still be desirable to provide a manual or patient activated modality which includes automatic atrial fibrillation detection to confirm the patient's own diagnosis. Hence, if the patient has a perceived atrial fibrillation episode and activates the defibrillator, it would be beneficial to the patient that the defibrillator, prior to cardioversion, confirm, through an atrial fibrillation detector, that atrial fibrillation is actually present. In this way, the patient will not be subjected to unnecessary cardioversion attempts which otherwise may cause discomfort to the patient and early depletion of the defibrillator power source.
Still other patients may benefit from a combined patient activated and fully automatic modality. For example, patients which are symptomatic some of the time would fall into this category. Such combined modalities must be coordinated and provide atrial fibrillation detection and confirmation to assure that unnecessary cardioversion attempts are not delivered. The present invention provides an atrial defibrillator which satisfies all of these requirements.